Method for providing a non-tacky film on tacky surfaces of polymeric materials



Feb. 15, 1966 R. J. HABERLIN 3,

METHOD FOR PROVIDING A NON-TAGKY FILM ON TACKY SURFACES 0F POLYMERIC MATERIALS Filed Oct. 1, 1962 F|G.4 FIGS linited States Patent METHOD FOR PROVIDING A NON-TACKY FILM 0N TACKY SURFACES OF POLY- MERIC MATERIALS Richard I. ll-Iaherlin, Weston, Mass., assignor to W. R. Grace 8: (10., Cambridge, Mass, a corporation of (Jonnecticut Filed Oct. 1, 11962, Ser. No. 227,441 11 Claims. (Cl. 117-6) This invention relates to a method for forming a nontacky film on normally tacky polymer, resin and rubber surfaces, and to the article produced thereby. In one aspect, it relates to the formation of a non-tacky film on the surface of such materials when they are deposited on non-absorptive sheets. In a particular aspect, it relates to forming a non-tacky film on the surface of tacky materials Which have been deposited on a sheet in a repeated pattern of a selected design, the individual patterns of which are subsequently cut or stamped into can ends, crown or lug caps, and a host of other sealing closure designs. In the latter use, the filmed material serves as the sealing gasket. In another aspect it relates to a onestep process for forming a non-tacky film on the surface of tacky materials and on the surface of the sheet on which they have been deposited.

Can end gaskets, for example, have been formed on punched can ends by nozzle lining. Such lining involves applying a fluid gasket-forming compound through a nozzle orifice to the edge of and while spinning the can end followed by drying, fluxing or curing of the compound. This method is well suited to lining round can ends but is not readily adaptable to lining irregularlysh-aped ends, such as those having square, rectangular, or oval shapes, for example.

A satisfactory alternate method has been developed for providing gaskets from liquid compositions for use on irregularly-shaped as Well as round closure elements. This method comprises disposing a liquid gasket-forming composition on a metal sheet in a repeated pattern of a selected shape or design, converting the composition to a form-stable gasket, and then cutting or stamping the shaped gasket. In essence, the particular shape is derived through the use of a cylindrical printing surface having the selected design or shape of the gasket incised therein in intaglio. The design is composed of a plurality of small, independent, non-communicating depressions formed by drilling, engraving, etching, or similar methods. In operation, the cylinder rotates over a bath of the liquid composition Where the composition is received by the depressions in the cylinder surface and transferred to a sheet, such as tin plate. The composition is transferred in the form of small individual dots in relief which, depending on the rheology of the composition, may immediately coalesce or may be made to flow together as by heating to form a continuous film. The step of transferring the composition from the printing cylinder to the sheet is referred to as printing. The printed compound is then set to a form-stable shape by any convenient method, such as heat, and the heat-treated sheet is then passed to a stack of similar printed sheets, and subsequently stamped.

A disadvantage attending the printing technique lies in the fact that the fluxed sealing composition which serves as the gasket exhibits a tacky surface. This is undesirable particularly where the sealing compositions are rubber based. Due to the natural tack of rubber, the printed sheets frequently stick together and will not feed to automatic stamping equipment. This, of course, requires interruptions in the stamping operation to separate the stuck sheets with consequent reductions in production rates. In addition, sections of the lined gaskets stick to the underside of a superposed printed sheet and give an irregular surface to the gaskets With poor sealing characteristics and, hence they must be discarded.

It is, therefore, an object of this invention to overcome the disadvantage of surface tack of normally tacky polymeric materials, and principally of such materials which are used in sealing closure elements. This objective is realized by forming a non-tacky, thin, organic film on the surface of the polymeric material. Briefly stated, the invention comprises applying an organic coating capable of forming a tack-free film on the normally tacky surface of a polymeric material and curing the coating on the material to form a film thereon. The polymeric material underneath the film remains in its original soft tacky condition. Accordingly, when a closure element containing the thus-filmed gasket is applied to seal a suitable container, the pressure involved in the sealing step ruptures the thin film and exposes the underlying tacky material to the mating surfaces which the material is intended to seal.

The film may be formed from conventional organic coating compositions as, from lacquers, varnishes or aqueous polymeric dispersions. A lacquer consists essentially of a film-forming resin and a volatile solvent with the principal film-forming ingredients being cellulose nitrate, ethyl cellulose, chlorinated rubber and the vinyl resins. Varnishes are unpigmented, oil-base paints composed of a solvent and binders of the leoresinous or synthetic type. The oleoresinous type of binder is generally comprised of drying oils in combination with natural or synthetic resins, chlorinated rubber, etc., whereas the synthetic type is normally comprised of alkyd resins and combinations of alkyd resins. Aqueous polymeric dispersions include gen erally emulsion-polymerized dispersions of vinyl chloridevinylidene chloride and styrene butadiene copolymers, as well as acrylic and vinyl acetate polymers and copolymers. The particular coating composition employed to form a film depends largely on the tack-free characteristics of the film and the end use of the filmed material.

The instant invention is particularly effective in providing a non-tacky film on compounds Which are used as gaskets in closure elements. These compounds usually consist of a colloidal system of complex composition. The liquid phase of the composition may be either aqueous or organic, such as, parafiinic hydrocarbons having a boiling point above F. The solid phase of the system generally comprises one or more of a variety of high polymers possessing elastomeric properties in varying degrees. Suitable polymers include such synthetic rubbers as butadiene-styrene copolymers, butad'iene-styrene-acrylonitrile terpolymer, and polychloroprene. Loading materials and substances which promote adhesion of the compound to tin plate also appear in the solid phase. Suitable additives include such fillers as channel black, titanium dioxide, calcium carbonate, and zinc oxide; and such resins as esterified gum rosin and polyterpenes.

conventionally, the surface of the metal on which the gasket-forming compound is printed is pre-coated with a lacquer, or the like. When the metal is fabricated into closures, the lacquer coated surface of the metal is used to form the internal surface of the closure to inhibit corrosion.

In the preferred embodiment of this invention, the metal is protected against corrosion and the tackiness of the surface of the gasket is overcome in one step. In brief, this embodiment comprises disposing a gasket-forming composition on the bare surface of metal, setting the composition to a form-stable material with a normally tacky surface, applying an organic coating capable of forming a tack-free film on the surface of the material and the metal on which. it is disposed, and curing the coating to form a film thereon.

The liquid gasket forming composition is usually set to a form-stable material by means of heat. Flash-drying the composition under infra-red light is satisfactory. Drying temperatures may vary depending on the liquid phase of the composition. Composition utilizing high boiling liquids such as high boiling paraffin oils may be dried at temperatures in the range of about 1200 to 1500 F. in about 8 seconds or less, whereas compositions utilizing low boiling liquids such as hexane may be dried at temperatures of 140 to 160 F. in 10 seconds or less. It is not necessary to completely evaporate the liquid phase of the composition before applying the coating. It is, in fact, preferred to allow a portion of the liquid phase to remain in the tacky material, i.e., about percent by weight. During the film-forming step, the remaining portion of the liquid will evaporate from the material and produce a crazed film. Such a film is desirable because it will rupture more easily during the sealing operation.

The method or means of applying the organic coating is not critical. Any type of coating mechanism or device which is capable of depositing a uniform amount in the desired thickness to the substrate may be employed. Special types which may be used include air knife coater,

- horizontal and vertical size presses, trailing blade, transfer roll, reverse roll, roller coater, gravure, bead coat, metering bar, spray coater and curtain coater. Deposition may be carried out in one or a number of applications and the amount deposited is such as to provide a film thickness ranging from about 0.1 to 0.2 mil (dry basis). Films having a thickness greater than 0.2 mil may be difficult to rupture during the sealing step, while those with a thickness less than about 0.1 mil may break apart under light pressure.

The method employed to cure the coating is dependent on its composition. For example, coatings of certain aqueous polymeric dispersions form continuous, adherent films when dried in air or in conventional drying apparatus. Coatings of conventional oleoresinous lacquers, however, must be baked in an oven to remove the solvent and to cure the oleroesinous component before satisfactory films are formed.

The invention is further illustrated by reference to the drawings in which:

FIGURE 1 schematically illustrates a printing process used to produce sealing gaskets.

FIGURE 2 is a perspective view of a printing cylinder having a can end design in intaglio.

FIGURE 3 shows a portion of a tin plate sheet bearing printed filmed gaskets.

FIGURE 4 shows a cross section of the tin plate and filmed gasket taken on line 4-4 of FIGURE 3.

FIGURE 5 shows a cross section of filmed tin plate sheet and gasket coated in one step.

Referring to FIGURE 1, a non-absorptive sheet 2, such as tin plate, and adapted to receive the gasket-forming composition is delivered from a feeder 3 containing a supply of blank sheets to a first conveyor belt 4. The conveyor moves the sheet to the printing site at which pressure roll 5 superimposed over rotating printing cylinder 6 are stationed. The surface of cylinder 6 is provided with a selected repeating pattern 7 (shown in FIGURE 2) incised in intaglio. As the cylinder rotates, its surface is immersed in a bath 8 of gasket-forming compound, disposed beneath cylinder 6, and the compound is received in the incised areas defining pattern 7. Suitable compounds are illustrated in Examples I to VI. Means, such as doctor blade 9, are provided to remove the compound which adheres to the cylinder surface.

Sheet 2 is then passed into the nip between roll 5 and cylinder 6 where the compound in the pattern is impressed onto the underside of the sheet. Movement and spacing of sheets on the conveyor 4 and the rotation of cylinder 6 are synchronized to effect a coincidental meeting of the sheet and the pattern 7. The imprinted sheet is then passed to the underside of a second conveyor belt 10 with the sheet being held magnetically in this position. Suitable attractive forces for holding the sheet on the underside of the belt may be developed by imbedding magnetic particles in the outerside of the belting. If an aluminum sheet is used, the magnetic force may be eliminated and such sheets may be held in place by vacuum instead.

The movement of conveyor belt 10 is guided upwardly by means of roll 11 and returned to a horizontal position as it passes over roll 12 which upturns the sheet 2. On its return passage to the cylinder 6, the belt 10 is directed downwardly by roll 13 and passed over roll 14 where it again follows a horizontal path. The upturned sheet may pass through a drying zone 15, depending on the constitution of the composition. For example, if the composition contains a solvent which must be eliminated, then a drying step would be required.

The imprinted sheet, dried or undried, then passes to the station 16 where an organic coating composition 17 is applied by suitable means, such as spray 18. The sheet is then passed through a heating zone 19 to cure the coating to form film 21. The polymeric material underneath the film remains in its original soft tacky condition, shown as 22 in FIGURE 4.

FIGURE 5 illustrates the preferred embodiment of the present invention wherein film 21 also covers sheet 2. The sheet 2 is then passed into receptacle 20 for storage.

Representative compounds which are useful in forming gaskets and coating compositions satisfactory for forming films thereon are illustrated in Examples I to VIII inclusive. All parts are by weight.

Example I This gasket-forming compound was comprised of 4.82 weight percent of low Mooney (20) -60 styrene-butadiene rubber, 3.16 percent of butadiene-styrene resin admixed with .02 percent channel black; 0.07 percent N,N di-beta-naphthyl para phenylenediamine, 6.31 percent titanium dioxide, 36.72 percent calcium carbonate, 2.19 percent esterified gum rosin, 2.19 percent polymerized beta-pinene and 43.82 percent of a parafiinic hydrocarbon boiling at 350 F.

The compound was deposited on the lacquered surface of tin plate which was then passed under infra-red lights. The compound was substantially dried to a tacky material for about 12 seconds at a temperature of about 1450 F.

An organic coating composition comprised of a solution of 3 grams of ethyl cellulose and 97 grams of ethyl alcohol was applied to the tacky surface of the material. The coating was deposited in an amount to yield a film 0.1 mil thick (dry basis). The coated material was baked in an oven at a temperature of about F. for about 45 seconds. A slightly crazed film enveloped the material.

Example 11 The procedure in this example was similar to that disclosed in Example I.

The gasket-forming material was comprised of a butadiene-styrene-acrylonitrile terpolymer dispersion containing rosin ester and filler and carried in a paraffinic hydrocarbon solvent.

The coating composition was comprised of a solution of 2 grams of methyl cellulose and 98 grams of water.

The coating was deposited on the tacky surface of the substantially dried material in an amount to yield a film 0.1 mil thick (dry basis). The coated material was dried in an oven at a temperature of about F. for about 1 minute. A slightly crazed film enveloped the material.

Example 111 The procedure of this example was similar to that disclosed in Example I.

The gasket forming material was the same as that described in Example II.

The coating composition was comprised of 200 grams polymerized rosin (Poly-pale Resin), grams maleic anhydride, 30.8 grams glycerin, 750 grams linseed oil, 1000 grams toluene, and 300 grams of a solution of mineral spirits, methyl ethyl ketone and methyl isobutyl ketone.

The coating was deposited on the tacky surface of the substantially dried gasket material in an amount to yield a film 0.1 mil thick (dry basis). The coated material was dried in an oven at a temperature of about 250 F. for about 1 /2 minutes. A slightly crazed film enveloped the material.

Example IV The procedure of this example was similar to that disclosed in Example II.

The gasket forming material Was the same as that described in Example II.

The coating composition was comprised of 338 grams of about a 20 percent solution of styrene-butadiene rubber (20 percent styrene and 80 percent butadiene, Buton 300) in xylol; 264 grams of a 33 percent solution of nitrocellulose in a solvent comprised of methyl ethyl ketone, toluene and alcohol; 6.4 grams of a percent solution of ethyl acid phosphate in alcohol; 50 grams methyl ethyl ketone, 75 grams toluene and 50 grams ethylene glycol monobutyl ether (butyl Cellosolve).

The coating was deposited on the tacky surface of the substantially dried gasket material in an amount to yield a film 0.1 mil thick (dry basis). The coated material was dried in an oven at a temperature of about 400 F. for about seconds. A slightly crazed film enveloped the material.

Example V This gasket-forming compound consisted of 8.73 weight percent of low Mooney (20) 40-60 styrene-butadiene rubber, .09 percent of N,N' di-beta-naphthyl-para-phenylenediamine, .02 percent channel black, .69 percent titanium dioxide, 3.93 percent talc, 23.04 percent calcium carbonate, 6.37 percent esterified gum rosin, 2.53 percent zinc resinate, .04 percent 0,0 dibenzamido diphenyl disulfied, and 54.59 percent of a parafiinic hydrocarbon boiling at 150 F.

The compound was printed on the bare surface of tin plate which was then passed under infra-red lights. The compound was substantially dried to a tacky material for about 12 seconds at a temperature of about 1450 F.

The heated tinplate was passed under a spray of a coating composition which was deposited on the tacky surface of the material and the printing surface of the plate in an amount to yield a film 0.2 mil thick (dry basis). The coating composition was comprised of 153 grams of vinyl chloride-vinyl acetate copolymer (Bakelite VMCH), grams of a polyester plasticizer (Plastol X), 300 grams methyl isobutyl ketone, 310 grams toluene, grams methyl ethyl ketone and 81 grams isophorone.

The coated substrate was baked in an oven at a temperature of about 350 F. for about 10 minutes. The film covering the gasket material and the tin plate was continuous, smooth, and adherent.

Example VI The procedure in this example was similar to that disclosed in Example V.

The gasket-forming compound was comprised of a butadiene-styrene rubber containing polymerized betapinene resin, filler and carried ina lower aliphatic hydrocarbon solvent. The compound was substantially dried to a tacky material for about 4 seconds at a temperature of 160 F.

The coating composition was comprised of 42.5 grams of a 50 percent solids vinyl toluene copolymer solution 0 in naphtha (Vintol 356V); 16.5 grams of a 60 percent solids vinyl toluene copolymer in naphtha. (Vintol 730- V), 20 grams tung oil (oxygenated), 30.5 grams mineral spirits, and 1.5 grams of a 6 percent ethanol solution of cobalt naphthenate.

The coating was deposited on the surface of the tacky material in addition to the surface of the plate supporting the material in an amount to yield a film 0.2 mil thick (dry basis). The coated substrate was dried in an oven at a temperature of about 350 F. for about 10 minutes. The film enveloping the gasket material and the tin plate was smooth and adherent.

When compressed under 25 pounds per square inch at F. for 24 hours, the filmed samples show no bonding or transfer to the covering plates. The samples which are not filmed, however, are solidly bonded to the covering plate due to the tacky surface.

Example VII The gasket forming composition of Example V was printed on strips of tinplate and substantially dried to a tacky material for about 12 seconds at a temperature of about 1450 F. The tacky material ranged in thickness from 3.5 to 4 mils.

The coating composition was a typical C enamel comprised of 200 grams polymerized rosin (Poly-pale Resin), 20 grams maleic anhydride, 30.8 grams glycerin, 5 grams zinc oxide, 750 grams linseed oil, 1000 grams toluene, and 300 grams of a solution of mineral spirits, methyl ethyl ketone and methyl isobutyl ketone.

The coating was deposited on the tacky surface of the gasket material in an amount to yield a film 0.1 to 0.2 mil thick (dry basis). The coated material was dried in an oven at a temperature of about 385 F. for about 5 minutes. A slightly crazed film enveloped the material.

The filmed samples were compressed in an arbor press at 40,000 p.s.i. This perpendicular pressure did not rupture the film enveloping the samples and there was no evidence of blocking.

Example VIII The procedure of this example was similar to that disclosed in Example VII.

The gasket forming material was the same as that described in Example VII.

The coating composition was comprised of a vinyl lacquer (CO-138).

The coating was deposited on the tacky surface of the gasket material in an amount to yield a film 0.1 to 0.2 mil thick (dry basis). The coated material was dried in an oven at a temperature of about 350 F. for about 10 minutes. A smooth continuous film enveloped the material.

The filmed samples were compressed in an arbor press at 40,000 p.s.i. This perpendicular pressure did not rupture the film enveloping the samples and there was no evidence of blocking.

Can tests covering filmed versus non-filmed can ends show that there is no significant difference in sealing performance. This is illustrated in the table below:

No. of cans which Gasket-forming compound: leaked per 1000 cans Example I (no film) 273 Example I (0.1 mil film) 264 Example III (no film) 238 Example III (0.l0.2 mil film) 210 Control sample 214 The table shows that no significant difference occurs in sealing properties between the filmed experimental compounds and those without films. In other words, a nontacky film on the gasket overcomes surface tack without impairing sealing performance.

While this invention is particularly described with respect to filming of can end gaskets, it will be appreciated by those skilled in the art that it may be applied to overcome the disadvantages of any normally tacky material. Thus, one side of a non-absorptive substrate may be coated with a normally tacky composition for subsequent use in preparing laminates thereof. It the coated individual substrates are to be stored for given periods of time, the surface of the composition can be provided with a non-tacky film according to this invention to avoid sticking of one to another in stacks. When the laminate is prepared, the film covering the composition will rupture under laminating pressures and expose the underlying tacky composition to the second substrate and provide a strong bond therebetween.

I claim:

1. A method of providing a non-tacky film on a normally tacky surface of an elastomeric gasket disposed on a metallic substrate which comprises applying an organic coating selected from the group consisting of 1) a lacquer,

(2) a varnish, and

(3) an aqueous dispersion of a film-forming polymer selected from the group consisting of (a) a vinyl chloride-vinylidene chloride copolymer,

(b) a styrene-butadiene copolymer,

(c) an acrylic resin,

(d) a vinyl acetate polymer, and

(e) methyl cellulose, and curing the coating on the gasket to form a tack-free film thereon having a thickness between about 0.1 to 0.2 mil which is rupturable so as to expose the underlying tacky surface of the gasket.

2. The method according to claim 1 wherein the coating is comprised of a lacquer.

3. The method according to claim 1 wherein the coating is comprised of a varnish.

4. The method according to claim 1 wherein the coating is comprised of an aqueous dispersion of a film-forming polymer selected from the group consisting of (a) a vinyl chloride-vinylidene chloride copolymer,

(b) a styrene-butadiene copolymer,

(c) an acrylic resin,

(d) a vinyl acetate polymer, and

(e) methyl cellulose.

5. A method of providing a tack-free surface on a sealing element which includes a metallic substrate and an elastomeric gasket having a normally tacky surface and composed of a pattern of a selected design disposed on a portion of said substrate which comprises applying over the tacky surface of the gasket and said substrate an organic coating selected from the group consisting of (1) a lacquer,

(2) a varnish, and

(3) an aqueous dispersion of a film-forming polymer selected from the group consisting of (a) a vinyl chloride-vinylidene chloride copolymer,

(b) a styrene-butadiene copolymer,

(c) an acrylic resin,

(d) a vinyl acetate polymer, and

(e) methyl cellulose, and curing the coating to form a tack-free film thereon having a thickness between 0.1 and 0.2 mil which is rupturable so as to expose the underlying tacky surface of the gasket.

6. The method according to claim 5 wherein the coating is comprised of a lacquer.

7. The method according to claim 5 wherein the coating is comprised of a varnish.

8. The method according to claim 5 wherein the coating is comprised of an aqueous dispersion of a film-forming polymer selected from the group consisting of (a) a vinyl chloride-vinylidene chloride copolymer,

(b) a styrene-butadiene copolymer,

(c) an acrylic resin,

(d) a vinyl acetate polymer, and

(e) methyl cellulose.

9. A closure comprising a metallic shell, an elastomeric gasket having a normally tacky surface disposed thereon and an organic tack-free film having a thickness between about 0.1 to 0.2 mil enveloping the gasket, said film being rupturable so as to expose the underlying tacky surface of the gasket and derived from an organic coating selected from the group consisting of 1) a lacquer,

(2) a varnish, and

(3) an aqueous dispersion of a film-forming polymer selected from the group consisting of (a) a vinyl chloride-vinylidene chloride copolymer, (b) a styrene-butadiene copolymer, (c) an acrylic resin, (d) a vinyl acetate polymer, and (e) methyl cellulose.

10. A closure according to claim 9 wherein the shell is tin plate.

11. A closure comprising a metallic shell, an elastomeric gasket having a normally tacky surface disposed thereon and an organic tack-free film having a thickness between about 0.1 and 0.2 mil enveloping the gasket and the exposed surface of the shell on which the gasket is disposed, said film being rupturable so as to expose the underlying tacky surface of the gasket and derived from an organic coating selected from the group consisting of (1) a lacquer,

( 2) a varnish, and

(3) an aqueous dispersion of a film-forming polymer selected from the group consisting of (a) a vinyl chloride-vinylidene chloride copolymer, (b) a styrene-butadiene copolymer, (c) an acrylic resin, (d) a vinyl acetate polymer, and (e) methyl cellulose.

References Cited by the Examiner UNITED STATES PATENTS 2,224,654 12/1940 McIntosh 11745 2,330,106 9/1943 Bernstein et al. 2,403,084 7/ 1946 James 11745 2,404,353 7/1946 Ash 1176 2,699,999 1/1955 Mahler 117-4 2,833,671 5/1958 Funk et al. 117-79 2,885,293 5/1959 Haskell et al. 2,915,413 12/1959 Ragan et al. 11738 2,957,784 10/ 1960 Schiefelbein. 3,030,229 4/1962 Esswein et al. 117-75 3,094,432 6/1963 Meyer-Jagenberg 11745 3,120,449 2/ 1964 Griswold l17--38 3,158,669 11/1964 Greenlie et al.

RICHARD D. NEVIUS, Primary Examiner. 

1. A METHOD OF PROVIDING A NON-TACKY FILM ON A NORMALLY TACKY SURFAACE OF AN ELASTOMERIC GASKET DISPOSED ON A METALLIC SUBSTRATE WHICH COMPRISES APPLYING AN ORGANIC COATING SELECTED FROM THE GROUP CONSISTING OF (1) A LACQUER, (2) A VARNISH, AND (3) AN AQUEOUS DISPERSION OF A FILM-FORMING POLYMER SELECTED FROM THE GROUP CONSISTING OF (A) A VINYL CHLORIDE-VINYLIDENE CHLORIDE COPOLYMER, (B) A STYRENE-BUTADIENE COPOLYMER, (C) AN ACRYLIC RESIN, (D) A VINYL ACETATE POLYMER, AND (E) METHYL CELLULOSE, AND CURING THE COATING ON THE GASKET TO FORM A TACK-FREE FILM THEREON HAVING A THICKNESS BETWEEN ABOUT 0.1 TO 0.2 MIL WHICH IS RUPTURABLE SO AS TO EXPOSE THE UNDERLYING TACKY SURFACE OF THE GASKET. 